Gas-purification process



APY l, 1930. D. 1 JAcoBsoN 1,752,382

GAS PURIFICATION PROCESS Filed Deo. 8, 1921 Cil Patented Apr. l, 1930UNITED STATES PATENT OFFICE DAVID L. JACOBSON, OF PITTSBURGH,PENNSYLVANIA, ASSIGNOR T THE KOPPERS COMPANY, 0F PITTSBURGH,PENNSYLVANIA. A CORPORATION 0F PENNSYLVANIA GAS-PURIFICATION PROCESSApplication led December 8, 1921. Serial No. 520,786.

This invention relates to the removal of hydrogen sulphide and othernoxious compounds, such as hydrocyanic acid, from gases containing them.Objects ot' the. invention are to eii'ect an eiiicicnt purilication ofthe gases with an absorbent liquid which removes the noxiousconstituents combined with revivitication of the absorbent liquid forfurther gas purification and disposal of substantially all the absorbedsulphur in a manner which avoids the escape ot' noxious fumes into theatmosphere in the vicinity of the gas purifying plant.

In addition to the general objects recited above, the invention has forfurther objects such other improvements or advantages 1n operation andresults as are found to obtain in the processes hereinafter descrlbed orclaimed.

In the accompanying drawing forming a part of this specification andshowing, for purposes of exemphiication a preferred form and manner inwhich the invention may be embodied and practiced, but Without limitingthe claimed invention specifically to such illustrative instance orinstances:

The ligure illustrates a diagrammatic representation of apparatus forcarrying out the improved -gas purifying process of the presentinvention. I n

In its present embodiment, the mventlon is applied to the purificationof fuel gases, such as coke oven gas: for convenience, the presentdescription will be confined to this use of the invention. Features ofthe invention are, however. readily susceptible of other valuableapplication; consequently, the scope of the invention is not confined tothe specitc use and specific embodiment herein described as anillustrative example.

In carrying out the invention, the gases, after the tar and ammonia havebeen removed, are brought into contact With a purifying solutionconstituted of dissolved nonvolatile alkali, Such as sodium carbonate orother soluble alkaline substances, the solution containing in suspensionan iron compound having an afinity for the sulphur absorbed by thealkali, such as iron oxide. Various iron compounds may be employed forthis through the solution line 4. In the scrubberV A, the gas is broughtinto contact with the purifying solution and the dissolved alkaliabsorbs the hydrogen sulphide and other noxious constituents of the gasforming soluble sulphide compounds. A further reaction takes placebetween the iron oxide and soluble sulphide compounds, with the resultthat iron sulphide forms and the soluble alkali is regenerated, thesoluble alkali acting as a carrier ofthe hydrogen sulphide to the ironoxide that is converted to iron sulphide. Some of the iron oxide mayalso react directly with the hydrogen sulphide.

The solution containing the absorbed impurities is then pumped from thesump D through a line 5 and discharged into the top of a second scrubberor washeuB. in which it is met by an ascending current of air. The airoxidizcs the iron sulphides to iron oxide and free sulphur.Concurrently, any sodium hydrogen sulphide which has escaped the actionof the iron will be decomposed by the sodium bicarbonate and anyabsorbed carbon dioxide will be expelled. '.l`hu`s. ail the absorbedgases are decomposed. The solution is thus regenerated or revivified forfurther puritication of the gas: the cycle of washing the impurities outof the gas and aerating the solution containing the iron oxide insuspension may be made continuous, as shovvn in the attached diagram ofthe apparatus used in the process. The revivified solution dischargesfrom the acrating scrubber B through the line (5 into a sump C fromwhich it may be pumped through the line 3 into the purification scrubberA. The concentration of thc ironoxide in suspension'and of the dissolvedalkali may be varied as desired; in practice, a one-half to one percentsodium carbonate solution, with tw o or three percent iron oxidesuspended init, will be found satisfactory. 'lhe suspension of ironoxide and iron sulphide in the alkaline solusumpD an tions are stored inthe sumps C and D, one, C, for the purification step, and the other, D,for the aerating step. In these sumpsl or tanks, air agitators or otheragitatng means may be provided. Preliminary agitation' of the spent washliquor accompanied by some regeneratin aeration is conducted in theAfurther regenerating aeration is effected in the scrubber B thateffects the thorough and intimate contact of air with flowing liquor.The conversion of the iron sulphide to iron oxide and free sulphur, andother action of the aiigmay take place partly or even to a large extent,in these tanks.

The chemical reactions taking' place in the purification scrubber may be'exemplified by the followingl equations (a) Absorption of .hydrogensulphide by` sodium carbonate.

NagCOs +I-I2S= NaI-1G03 -l- NaI-IS Carbon dioxide, if present, is alsoabsorbed.

NagCOs -l-I-LO CO2=2NaHCO3 Direct absorption of hydrogen sulphide by'iron oxide.

F8203 i Fe2s3 i" (b) Action of sodium hydrogen sulphide and sodiumbicarbonate on iron oxide forming iron sulphide:

rezsffauazcoanzo In the aerating steps, the chemical reactions areexemplified in the following eolua'4 tions:

(a) Oxidation of iron sulphide to iron oxide and free sulphur:

2Fe2s3+3o2=2re2o3+es (b) Conversion of bicarbonate to carbon- (c) Actionof bicarbonate on sodium hydrogen sulphide:

1921, Serial No. 462,136. Where a very rapid thiosulphate formation isnot desired, such formation can be decreased by employing very dilutevsolutions, such as one-half percent sodium carbonate or less. A furtherad-f -in the suspension, part of the sludge being withdrawn at suit letimes for recovery of the sulphur and iron oxide. AFrom time to time,fresh iron hydroxide may be added; alternativel iron sulphide may'beadded at a point be ore' the air treatment and such Y treatment willconvert the iron sul hide to iron oxide. The concentration of 'ssolvedalkali may also be maintained by periodical additions.

The solution containing the suspension will also remove hydrocyanic acidfrom the gas; this may go into chemical combination with the ironcompounds. Otherwise the hydroc anic acid will ass out to some extentwith t e airused in t e aeratin'g step. l

The purification process is carried'out in 5 the above describedexemplification by means of a suspension of iron oxide in an alkalinesolution. This washing mixture maybe obtained by means of a number ofmaterials which have essentially the same effect in carrying out thereactions described. Instead of iron oxide, ferrie carbonate or basicferrie carbonate may be employed; or the iron may be in the form offerrie hydroxide. Ferrous compounds may also be used instead of 'theiron oxide, either in the form of ferrous oxide, ferrous carbonate orbasic carbonate, or ferrous hydroxide; the ferrous compounds will havean action similar to the ferrie oxide, and at the same time the aeratingprocess will graduall transform them to the ferrie state. The dissolvedalkali may be any substance which gives an alkaline reaction to thesolution, such as the carbonates of sodium and potassium, orthe'hydroxides of sodium and potassium; oralkaline magnesium or calciumcompounds, such as magnesium hydroxide and magnesium carbonate may beadded to the suspension, which have the same effect of rendering thesolution alkaline.

The invention as hereinabove set forth may be variously embodied withinthe scope of the claims hereinafter made.

What is claimed is:

1. In a process of purifying gases containing hydrogen sulphide, thecombination of steps which consists in: washing the gas with an alkalinesolution containing an iron compound having an affinity for sulphur; andthen passing the spent wash-liquor through a plurality of successivedifferin regeneration treatment stages, in the first o whichv a body ofsaid liquor is subjected to a preliminary agitation accompanied bregenerating aera tion and is thereafter su jected to a regeneratingaeration that effects a thorough and intimate contact of air with theflowing 1i uor.

2. A process as claimed in claim 1, 1n W ich the alkaline solution is asodium carbonate solution and in which the contained iron compound isiron oxide.

In testimony whereof I have hereunto set my hand.

DAVID L. JACOBSON.

